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I'm sort of enjoying this struggle a little. But it is hard getting the head
around this functional programming paradigm. I came across a beautiful implementation of a sum: function sum(list, i = 0) = i < len(list)  1 ? list[i] + sum(list, i + 1) : list[i]; works a char. I want to calculate a cumulative sum, using a generator of course such that each element in the new vector is the sum of all previous vectors and itself. But I figured a place to start is to fix the sum above which works forwards to one that works backwards. To clarify the sum above appears to me. Takes a sample vector V=[1, 2, 3]: sum(V) = 1 + 2 + 3 sum(V,1) = 2 + 3 sum(V,2) = 3 I wanted just as an exercise to reverse this logic, so that: sum(V) = 3 + 2 + 1 sum(V,1) = 2 + 1 sum(V,2) = 1 I don't NEED this, it was just an idea as you can see a cumulative sum in that output emerging already. So I tried: function sum(list, i = 0) = i < len(list)  1 ? list[len(list)1i] + sum(list, i + 1) : list[len(list)1i]; and if I single step this in my mind it seems right: sum(V) = 3 + sum(V,1) sum(V,1) = 2 + sum(V,2) sum(V,2) = 1 but OpenSCAD returns a result of ... 8. Clearly I've misunderstood something. Of course as noted this isn't essential. It's an exercise. My goal is to get a vector of cumulative sums back. Regards, Bernd.  Sent from: http://forum.openscad.org/ _______________________________________________ OpenSCAD mailing list [hidden email] http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org 
Here’s one implementation of a cumulative sum: https://github.com/revarbat/BOSL2/blob/e32735296cc173890a549f73d8506224af2eef8e/math.scad#L458 Revar On Apr 28, 2020, at 1:16 AM, ThumbOne via Discuss <[hidden email]> wrote:
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Your question made me remember my own steps years ago. Those challenges are a right track to master the unique nature of OpenSCAD. I see no trouble with your solution. After all, the following: echo(sum([1,2,3])); echo(sum([1,2,3],1)); echo(sum([1,2,3],2)); results in: ECHO: 6 ECHO: 3 ECHO: 1 for your later version of sum(). How have you gotten 8? Em ter., 28 de abr. de 2020 às 09:16, ThumbOne via Discuss <[hidden email]> escreveu: I'm sort of enjoying this struggle a little. But it is hard getting the head _______________________________________________ OpenSCAD mailing list [hidden email] http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org 
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I can't see anything wrong with that code, assuming the words all mean what I
think they mean, apart from it's going backwards ;) I don't know OpenSCAD very well, but I'm not too bad at programming. Here's my full program: function sum(list, i = 0) = i < len(list)  1 ? list[len(list)1i] + sum(list, i + 1) : list[len(list)1i]; echo( sum([1,2,3]) ); echo( sum([10, 8, 6]) ); And here's the output when I press F5: ECHO: 6 ECHO: 24 That looks fine to me. Bit of "debugging"... function sum(list, i=0) = let ( result = dosum(list, i) ) echo(str("sum(", list, ", ", i, " = ", result) ) result; function dosum(list, i) = i < len(list)  1 ? list[len(list)1i] + sum(list, i + 1) : list[len(list)1i]; echo( sum([1,2,3]) ); echo( sum([10, 8, 6]) ); Result: ECHO: "sum([1, 2, 3], 2 = 1" ECHO: "sum([1, 2, 3], 1 = 3" ECHO: "sum([1, 2, 3], 0 = 6" ECHO: 6 ECHO: "sum([10, 8, 6], 2 = 10" ECHO: "sum([10, 8, 6], 1 = 18" ECHO: "sum([10, 8, 6], 0 = 24" ECHO: 24  The University of Glasgow, charity number SC004401 On Tuesday, 28 April 2020 11:25:41 BST Revar Desmera wrote: > So I tried: > > function sum(list, i = 0) = i < len(list)  1 ? list[len(list)1i] + > > sum(list, i + 1) : list[len(list)1i]; > > > > and if I single step this in my mind it seems right: > > > > sum(V) = 3 + sum(V,1) > > sum(V,1) = 2 + sum(V,2) > > sum(V,2) = 1 > > > > but OpenSCAD returns a result of ... 8. _______________________________________________ OpenSCAD mailing list [hidden email] http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org 
OK, so I left the ')' out of the echo, but you get the gist. Do I get a B? ;)
echo(str("sum(", list, ", ", i, " ) = ", result) ) On Wednesday, 29 April 2020 13:14:08 BST Dr Nicholas Bailey wrote: > echo(str("sum(", list, ", ", i, " = ", result) ) _______________________________________________ OpenSCAD mailing list [hidden email] http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org 
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You may want to browse
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Tips_and_Tricks & examine some of the https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Libraries#Other_Libraries  Admin  email* me if you need anything, or if I've done something stupid... * click on my MichaelAtOz label, there is a link to email me. Unless specifically shown otherwise above, my contribution is in the Public Domain; to the extent possible under law, I have waived all copyright and related or neighbouring rights to this work. Obviously inclusion of works of previous authors is not included in the above.  Sent from: http://forum.openscad.org/ _______________________________________________ OpenSCAD mailing list [hidden email] http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
OpenSCAD Admin  email* me if you need anything, or if I've done something stupid...
* on the Forum, click on my MichaelAtOz label, there is a link to email me. Unless specifically shown otherwise above, my contribution is in the Public Domain; to the extent possible under law, I have waived all copyright and related or neighbouring rights to this work. Obviously inclusion of works of previous authors is not included in the above. 
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